This specification is to be read in conjunction with our prior international applications PCT/AU01/00247, PCT/AU02/01129, PCT/AU04/00242 relating to SODAR systems using long pulses encoded in a ‘pulse compression’ manner, using over-sampling of received echoes for good resolution and processing gain, and using complex Fourier-domain processing of the sampled echoes to achieve further discrimination and processing gains in the signal-to-noise ratio. The pulses—generically called ‘chirps’—employed in our prior inventions preferably had durations in the order of tens of seconds. The pulse-compression technique employed was preferably a linear increase or decrease in phase (tone) over the duration of the pulse; for example, a steady increase in tone from 500 to 1500 Hz, or a steady decrease in tone from 1500 to 500 Hz. The methods disclosed involved ‘listening while sending’; that is, echoes are received and processed while transmission of the chirp is still under way. This technique not only allows very high system and processing gains that result in exceptionally good s/n (signal to noise ratio), but it also enables atmospheric discontinuities that occur close to the ground to be detected. Since prior art systems could not ‘listen while sending’, it was necessary to use short powerful pulses for short-ranges and to suffer the resulting very poor system and processing gains. Such prior art SODARs were essentially incapable of detecting and displaying wake vortices with the high spatial and temporal necessary for charactreising the vortices in a wide range of airport environments.
While the SODAR systems disclosed in our prior applications were capable of detecting wake vortices and of monitoring wind conditions in the vicinity of airports with much greater sensitivity and precision than was previously possible in the art, they still had difficulty in displaying the ‘life’ of a vortex; for example, tracking the wind shear disturbances formed by a landing aircraft as they form, fade, travel to the ground or dissipate over a period of seconds or minutes.
For brevity, the disclosures in our aforementioned applications are regarded as being incorporated herein, including the extensive discussion of the prior art contained in the specifications of those applications. In addition, some of the terminology that is used herein is explained or defined in those specifications.